SDN: Physical vs. Logical

A popular philosophical argument for rationalizing the claims of religion and science states that they represent non-overlapping magisteria — in essence, positions held about one are irrelevant to the other since the two deal with irreconcilable metaphysical realms. Which brings us to the debate over how best to build software-defined and -controlled networks: Is there separation between physical and virtual elements? Should there be?

On one side we have SDN for physical networks, based on control of forwarding decisions and even topological connections among switches and routers via OpenFlow. On the other, we have virtual network overlays that create logical networks using virtual switches and layer virtual network application services (think firewalls, load balancers, VPN gateways, WAN optimizers) on top of the existing physical infrastructure.

Both approaches can programmatically manipulate network traffic, automate configurations and insert network services using a controller and APIs — the exact definition of SDN. But they’re dramatically different in ease of implementation and integration with, and control over, existing network equipment and virtual server environments.

While SDN has been synonymous with OpenFlow and centralized software control over physical network flows, that’s changing. Partly it’s because network pros are gaining an understanding of various overlay approaches, but it helps that the big kahuna in enterprise virtualization, VMware, has released its own overlay-based network virtualization product, NSX. In this report we’ll examine the features, benefits and drawbacks of software virtualized networks; contrast them with physical, OpenFlow-based SDN; and offer some advice on how to get started virtualizing and programmatically controlling your environment by building on what you already have: virtual servers, a flat network fabric and widely used system management tools. (S7370913)